I think the intent was it is a cover. I haven't gotten one with either of my AHPC boats. The hulls come wrapped in bubble wrap and in a box.

They do look cool though, and they do keep grime off the boat, but a friend destroyed his towing through a thunderstorm with some extreme wind (almost flipped the trailer over), and rain. Not sure if that is mis-use or just not a great product. Hard to say. It did hold up to a few trips to Florida, so....

(edit)-Personally I don't care for covers while trailering. There's too much room for something to flap around while going down the road, and if you get some sand in there, or a sharp rock it could really raise hell with the finish. The best thing you can do is get a trailer that protects your boat from stuff getting kicked up by the tow vehicle.